To meet the demand for wireless data traffic, which has increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long-term evolution (LTE) system’.
It is considered that the 5G communication system will be implemented in millimeter wave (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To reduce propagation loss of radio waves and increase a transmission distance, a beam forming technique, a massive multiple-input multiple-output (MIMO) technique, a full dimensional MIMO (FD-MIMO) technique, an array antenna technique, an analog beam forming technique, and a large scale antenna technique are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a device-to-device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, and the like.
In the 5G system, a hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and a sliding window superposition coding (SWSC) as an advanced coding modulation (ACM) scheme, and a filter bank multi carrier (FBMC) scheme, a non-orthogonal multiple Access (NOMA) scheme, and a sparse code multiple access (SCMA) scheme as an advanced access technology have been developed.
Communication systems have been developed to support a higher data rate to meet ever-increasing demand for radio data traffic.
Meanwhile, communication systems proposed up to now have developed various schemes for mainly improving a spectral efficiency for increasing a data rate, however, it is difficult to satisfy explosive demand for radio data traffic with only the schemes for improving the spectral efficiency.
So, various schemes have been proposed for satisfying the explosive demand for the data traffic, and a typical one is a scheme of using a very wide frequency band, e.g., an mmWave frequency band.
It is very difficult to obtain a wide frequency band in a frequency band (<5 GHz) used in a current mobile communication cellular system, so there is a need for obtaining an mmWave frequency band in a frequency band higher than the frequency band used in the current mobile communication cellular system.
However, in a general wireless communication system, the higher a frequency band used for a wireless communication is, the more increased propagation path loss is. So, a propagation distance is relatively short due to increase of this propagation path loss, so it results in decrease of a service coverage. So, various schemes for solving a service coverage decrease problem due to increase of propagation path loss, that is, for mitigating propagation path loss and increasing a propagation distance have been proposed, and a typical one is a beam-forming scheme.
A scheduled access process in a communication system supporting a general beam-forming scheme will be described with reference to FIG. 1.
FIG. 1 schematically illustrates a scheduled access process in a communication system supporting a general beam-forming scheme.
Referring to FIG. 1, a scheduled access process denotes an access process for a base station to determine a location of a uplink resource, uplink resource amount, and a uplink transmission timing which are to be used for a user equipment (UE) to transmit data.
First, a UE 111 transmits uplink data to a base station (not shown in FIG. 1) based on resource allocation information related to a uplink resource allocated from the base station to the UE 111 and transmission timing information about a uplink transmission timing determined for the UE 111. This will be described below.
First, the UE 111 receives scheduling information from the base station through a physical downlink control channel (PDCCH). Here, the scheduling information includes resource allocation information related to a uplink resource allocated from the base station to the UE 111 and transmission timing information about a transmission timing determined for the UE 111.
After receiving the scheduling information, the UE 111 detects that there is a data packet to be transmitted at operation 113, and transmits a scheduling request (SR) packet to the base station at a corresponding timing through a corresponding resource based on the scheduling information received from the base station at operation 115. Here, the scheduling request packet is transmitted based on a corresponding beam at a corresponding location of a random access channel (RACH) allocated to the UE 111.
The UE 111 receives a scheduling grant and resource allocation information from the base station at operation 117. The UE 111 transmits the data packet to the base station through a physical uplink shared channel (PUSCH) corresponding to the resource allocation information at operation 119.
If the scheduled access scheme as described above is used, a base station may allocate a uplink resource which is optimal for a UE, so efficiency of a resource may be increased.
However, the scheduled access scheme has a requirement that the base station needs to exactly know buffer status and channel status for all UEs to which the base station provides a service. Here, the channel status at least includes beam-forming information.
Therefore, if the requirement is not satisfied, the scheduled access scheme may result in the following inefficiency.
(1) There is a probability that a uplink resource will be allocated to a UE which has no data to be transmitted, or a probability that more uplink resources than necessary will be allocated to a UE which has no data to be transmitted.
(2) There is a probability that a modulation and coding scheme (MCS)(or a beam resource) which is unsuitable for channel status of a corresponding UE will be allocated.
(3) Gain of a scheduling scheme among a plurality of UEs which is based on channel quality information may be decreased. Here, the scheduling scheme which is based on the channel quality information may be, for example, a proportional fair (PF) scheduling scheme.
Further, if the scheduled access scheme is applied to an mmWave communications system supporting a beam-forming scheme, the following situation may occur.
(1) First, in the mmWave communication system supporting the beam-forming scheme, a channel relatively fast changes and a beam dimension increases, so amount of feedback information increases and a feedback period may be shortened. This results in increase of control channel overhead and power consumption of a UE.
(2) If the mmWave communication system supporting the beam-forming scheme transmits a control packet of a relatively small size such as a buffer status report packet, system efficiency may be decreased, and this is a limitation of spatial domain multiplexing.
A scheduled access process in a communication system supporting a general beam-forming scheme has been described with reference to FIG. 1, and operating processes of a base station and UEs according to a scheduled access process in a communication system supporting a general beam-forming scheme will be described with reference to FIG. 2.
FIG. 2 schematically illustrates operating processes of a base station and UEs according to a scheduled access process in a communication system supporting a general beam-forming scheme.
Referring to FIG. 2, a base station 211 transmits scheduling information in a specific radio frame, e.g., the first radio frame among downlink radio frames at operation 217. Each of UEs which receives a service from the base station 211, e.g., a UE #1 213 and a UE #2 215 receives scheduling information transmitted by the base station 211, and transmits a scheduling request packet based on the scheduling information at operations 219 and 221. Here, a location of a resource in which each of the UE #1 213 and the UE #2 215 transmits the scheduling request packet, i.e., a location within an RACH is fixed.
The base station 211 determines a UE which the base station 211 will allocate a uplink resource based on the scheduling request packet received from each of the UE #1 213 and the UE #2 215, and allocates the uplink resource to the determined UE. In FIG. 2, it will be assumed that the base station 211 allocates the uplink resource to the UE #1 213. So, the base station 211 transmits scheduling information including information related to the uplink resource allocated to the UE #1 213 at operation 223. Upon receiving the scheduling information transmitted by the base station 211, the UE #1 213 transmits a data packet to the base station 211 through a corresponding uplink resource at a corresponding timing based on the received scheduling information at operation 225.
Upon detecting that data packet transmitting operation of the UE #1 213 is completed, the base station 211 allocates a uplink resource to the UE #2 215, and transmits scheduling information including information related to the uplink resource allocated to the UE #2 215 at operation 227. Upon receiving the scheduling information transmitted by the base station 211, the UE #2 215 transmits a data packet to the base station 211 through a corresponding uplink resource at a corresponding timing based on the received scheduling information at operation 229.
As described in FIG. 2, if the scheduled access process is used, delay time increases due to transmission/reception of a scheduling request packet, and/or the like, a UE needs to continuously monitor scheduling information transmitted from a base station, so consumed power thereof may be increased. Further, a retransmission operation for a corresponding packet may be inefficient. That is, a retransmission process such as a hybrid automatic repeat request (HARQ) process is required, a scheduling request packet transmitting/receiving operation is performed while the retransmission process is performed, so a buffer size as well as delay time increases.
Meanwhile, a random access process in a communication system supporting a general beam-forming scheme will be described below.
First, the random access process denotes an access process in which a UE which occupies a RACH based on a contention-based scheme transmits a data packet if there is data to be transmitted at a buffer included in the UE.
In the random access process, amount of buffer status report packets and channel status feedback information decreases, so resources used for data packet transmission/reception may increase, this results in increase of resource efficiency.
Even though the random access process needs to perform a beam-forming process for a corresponding beam, a UE which is located at a corresponding location may perform a random access process, so a base station may not know about that which UE will perform a random access process in advance.
Of course, if a base station performs an omni-directional beam search process, the base station may perform a random access process with the UE regardless of that the UE is located at which direction. However, for performing the omni-directional beam search process, the base station needs to use an omni-directional beam pattern, and use of the omni-directional beam pattern may decrease beam-forming gain. For example, if the omni-directional beam pattern is used, an arrival distance may be reduced to ¼ compared to a case that the omni-directional beam pattern is not used.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.